1. Field of the Invention
The present invention relates to an image recording apparatus for recording an image on a printing plate, and particularly to an image exposure apparatus having a mechanism for performing the positioning in a state that the printing plate is put on a plate feed guide.
2. Description of the Related Art
The conventional image exposure apparatus is to record (expose) an image on a printing plate consisting of an aluminum foil sheet. In the image exposure apparatus, a plate feed conveying section is provided with a reversing unit and a conveyer. The reversing unit transmits to the conveyer a printing plate drawn out from a cassette through rolling up on a reversing roller. The conveyer conveys obliquely below the printing plate put on a conveying belt while supporting the printing plate in cooperation with the roller so that the top of the printing plate is in contact with a pin roller. When the printing plate is in contact with the pin roller, the plate feed conveying section causes a positioning motor to operate so that the reversing unit moves together with the conveyer on a parallel basis. Thus, the printing plate is in contact with the pin roller to perform the positioning of the printing plate. The printing plate subjected to the positioning is fed to a puncher by the conveyer in the leading edge (cf. for example, Japanese Patent Application Laid Open Gazette TokuKai. 2001-356489 (Page 1, FIG. 2).
According to the image exposure apparatus as mentioned above, the printing plate, which is put on a plate feed guide formed as a plate, is conveyed to a punch section to form punched holes on the printing plate through performing a punch processing. The punched holes are used for a determination of positioning in a printing processing, which is the continuation step. The printing plate, which is put on the plate feed guide, is conveyed to an exposure section and is wound on a rotating drum of the exposure section. Then the printing plate is subjected to an exposure processing.
By the way, there is a necessity for making sure of reproduction quality of exposure recording positions, in which the exposure recording positions on a plurality of printing plates are given with uniformity in its entirety. For this reason, before the exposure processing by the exposure section, there is performed the following positioning in a state that the printing plate is put on the plate feed guide.
As shown in FIG. 9, there is performed a first positioning in such a manner that a printing plate 12 is put on a plate feed guide 20, a front edge of the printing plate 12 is in contact with a pair of positioning pins 48 located in the vicinity of a punch section (not illustrated), the printing plate 12 is conveyed in a horizontal direction through pushing a left end edge of the printing plate 12 by a conveying pin 42, and a right end edge of the printing plate 12 is contact with a reference pin 36 provided on the plate feed guide 20. At this position, there are formed punched holes 49a and 49b in the front edge portion of the printing plate 12. Next, after the front edge portion of the plate feed guide 20 is rotatably moved to be lowered, there is performed a second positioning in such a manner that the front edge of the printing plate 12 is in contact with at least a pair of positioning pins 52 provided on a rotating drum (not illustrated), and the right end edge of the printing plate 12 is in contact with the reference pin 36 provided on the plate feed guide 20. Thereafter, the printing plate 12 is wound on the rotating drum to perform the exposure processing.
Since the printing plates 12 are different in their size, there is a need that the reference pin 36 alters its position to meet a size of the plate. For example, the smaller size of the printing plate, the reference pin 36 is located more inside (the nearer left in FIG. 9) the plate feed guide 20. For this reason, a starting position of the reference pin 36 is detected by a home position sensor S1 or S2, and the reference pin 36 is moved inside by a predetermined distance from the position of the home position sensor S1 or S2 so that the reference pin 36 is set up to a position according to the size of the printing plate.
As mentioned above, the plate feed guide 20 reciprocates between a position (a) of FIG. 9 and a position (b) of FIG. 9 in which the plate feed guide 20 rotatably moves in such a manner that the front portion is lowered. Owing to variation (because of variation of the reciprocating track by mechanical errors and other causes) of reproduction quality of exposure recording positions when the rotatable movement operation is repeated, it is difficult to expect a complete coincidence of the position of the plate feed guide 20 between the position (a) of FIG. 9 and the position (b) of FIG. 9. And thus it may happen that variation (several tens to several hundreds of μ meters) of minor discrepancy Δx is generated. With the discrepancy of the plate feed guide 20, the home position sensor S1 or S2 also shifts by the same amount Δx, and thus the reference pin 36 also shifts by the same amount Δx. As a result, the printing plate 12 also shifts by Δx in a punch position and an exposure position, so that the punched holes 49a and 49b are wound on the rotating drum and exposed in a state that the punched holes 49a and 49b also shift by Δx.
The reproduction quality of positions of an image on the printing plate 12 needs about 50μ meters or less where a position of a punched hole on the printing plate 12 is selected as the criterion. Thus, in some variation due to mechanical errors and the like of the plate feed guide 20, it would be difficult to make sure of the reproduction quality of positions of an image.